Ixbt-Labs has done some comparisons and came to the conclusion that
ANY Duron from week 36 on will do 1GHz.
They have a chart with some of the speeds/weeks that they have tested with results. You need to scroll down the page to the chart.
Edit: Finally figured out what I did wrong in the URL and repaired it.
This chart is basically the same as in the link posted below, except for actually stating a specific week here.
